Valve assemblies having a pressure responsive main valve member operated by a low force, short travel pilot valve actuator are relatively well known in the art. A low force short travel actuator permits a valve of this type to be operated by a low wattage solenoid or by a magnetic latch type device. These are important aspects for a valve used in conjunction with the ever growing electronic control field where low wattage devices are always an advantage, or where a valve assembly may be adaptable to a magnetic latch type actuator for battery operation. Valves of the type described are commercially available in a number of configurations, but due to their more complicated structure, bulk, and high cost, have not gained a wide acceptance in the market place. It is therefore the primary object of this invention to provide a pilot operated valve assembly of simple construction, compactness, economical manufacturing cost and one that can operate with a low force, short travel pilot actuator and that by the foregoing stated criteria, would gain a greater acceptability over present types now available.
To meet the simplicity object, in one aspect the present invention was developed as an improvement over the construction of the valve described in U.S. Pat. No. 3,672,627 to W. R. McCarty, Jr. et al. Although the McCarty patent is of simple construction and operates with small actuation forces, it also needs a pilot actuator that requires a large actuator travel that limits its capability for achieving low operational power and for adaptability to magnetic latch operation. An attempt to reduce the power consumption of a long actuator travel pilot valve is described in U.S. Pat. No. 4,502,661 to Wesley S. Swanson. Although this valve operates at lower continuous power levels than that shown by McCarty, the long actuation stroke required at its initial energization requires a high power spike which in some applications could be undesirable. The added pole piece also adds a little more complexity over the McCarty valve, but still requires a similar lengthy stroke and thereby limits its adaptability to be an efficient magnetic latch type actuator. The valves shown by McCarty and Swanson are simple, compact, and economical to manufacture, but due to their large actuator travel requirements, do not meet the desired objects of the invention.
U.S. Pat. No. 4,283,040 to L. Kolze, describes a valve where the pilot valve actuator does provide the low force and short actuator travel requisite, is relatively compact, but is more complicated and costly to manufacture and thereby does not fully meet the present invention objectives. Other valves meeting the performance criteria of low force and short pilot actuator travel are those similar to that shown in FIG. 3 of this application, where the pilot actuator is offset from the pressure responsive main valve member. These valve designs are bulky, complex, and costly to manufacture. As shown in FIG. 3 which illustrates the prior art, location of the pilot valve spaced apart from the main valve creates a structure where pilot and bleed passages are difficult to economically fabricate and the need for special orientation to assemble asymmetrical parts adds to the cost. Also, these valves use seal gasketing that is not symmetrical and can cause some difficulty to obtain uniformity of gasket sealing pressure that could lead to seal leakage. The FIG. 3 valve utilizes the eccentric pilot location with respect to the pressure responsive main valve member to obtain a short pilot actuator travel over that required by the McCarty and Swanson valves, but at the expense of complexity, size, and cost. Thus, all the above valve assemblies described are deficient in some aspect of the objectives achieved by the present invention which will be more fully understood from the Summary of the Invention below and Detailed Description that follows.